[Sync] Always check the device info provider for being null before using it.

[Sync] Always check the device info provider for being null before using it.

During sign out, the DeviceInfoProviderImpl is reset before 
DeviceInfoSyncService is told we're shutting down, as well as in a
separate task. This means if we get extremely unlucky, and a pulse is
happening at just the right time, we'll try to use the provider after
it's been destroyed. To fix this, we can just check that it's not
nullptr before using it. The other usages of the provider in
DeviceInfoSyncService have stronger guarantees from sync that we're not
in shutdown yet, and as such they DCHECK instead.

No unit tests were added as part of this change. It is non-trivial to
force an asyc pulse, and we currently do not have good seams to allow
this. Since this change needs to be merged back, I want this
modification to be as small as possible.

BUG=709927
Review-Url: https://codereview.chromium.org/2810873005
Cr-Commit-Position: refs/heads/master@{#463814}
Committed: https://chromium.googlesource.com/chromium/src/+/babffd17e43935e30657dcfda02d962791adf460

[skym, 2017-04-11 17:58:06]

Description was changed from

==========
[Sync] Always check the device info provider for being null before using it.

BUG=709927
==========

to

==========
[Sync] Always check the device info provider for being null before using it.

During sign out, the DeviceInfoProviderImpl is reset before 
DeviceInfoSyncService is told we're shutting down, as well as in a
separate task. This means if we get extremely unlucky, and a pulse is
happening at just the right time, we'll try to use the provider after
it's been destroyed. To fix this, we can just check that it's not
nullptr before using it. The other usages of the provider in
DeviceInfoSyncService have stronger guarantees from sync that we're not
in shutdown yet, and as such they DCHECK instead.

No unit tests were added as part of this change. It is non-trivial to
force an asyc pulse, and we currently do not have good seams to allow
this. Since this change needs to be merged back, I want this
modification to be as small as possible.

BUG=709927
==========

[skym, 2017-04-11 17:58:06]

skym@chromium.org changed reviewers:
+ pavely@chromium.org

[skym, 2017-04-11 17:58:11]

The CQ bit was checked by skym@chromium.org to run a CQ dry run

[skym, 2017-04-11 17:58:14]

PTAL

[commit-bot: I haz the power, 2017-04-11 17:59:00]

Dry run: CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2017-04-11 18:48:17]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2017-04-11 18:48:18]

Dry run: This issue passed the CQ dry run.

[pavely, 2017-04-11 22:34:26]

lgtm

[skym, 2017-04-11 22:35:48]

The CQ bit was checked by skym@chromium.org

[commit-bot: I haz the power, 2017-04-11 22:36:46]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2017-04-11 22:47:30]

CQ is committing da patch.

Bot data: {"patchset_id": 1, "attempt_start_ts": 1491950148667740, "parent_rev":
"cbb485045d95ea0934cce5a99e3796d4dcbfb596", "commit_rev":
"babffd17e43935e30657dcfda02d962791adf460"}

[commit-bot: I haz the power, 2017-04-11 22:48:21]

Description was changed from

==========
[Sync] Always check the device info provider for being null before using it.

During sign out, the DeviceInfoProviderImpl is reset before 
DeviceInfoSyncService is told we're shutting down, as well as in a
separate task. This means if we get extremely unlucky, and a pulse is
happening at just the right time, we'll try to use the provider after
it's been destroyed. To fix this, we can just check that it's not
nullptr before using it. The other usages of the provider in
DeviceInfoSyncService have stronger guarantees from sync that we're not
in shutdown yet, and as such they DCHECK instead.

No unit tests were added as part of this change. It is non-trivial to
force an asyc pulse, and we currently do not have good seams to allow
this. Since this change needs to be merged back, I want this
modification to be as small as possible.

BUG=709927
==========

to

==========
[Sync] Always check the device info provider for being null before using it.

During sign out, the DeviceInfoProviderImpl is reset before 
DeviceInfoSyncService is told we're shutting down, as well as in a
separate task. This means if we get extremely unlucky, and a pulse is
happening at just the right time, we'll try to use the provider after
it's been destroyed. To fix this, we can just check that it's not
nullptr before using it. The other usages of the provider in
DeviceInfoSyncService have stronger guarantees from sync that we're not
in shutdown yet, and as such they DCHECK instead.

No unit tests were added as part of this change. It is non-trivial to
force an asyc pulse, and we currently do not have good seams to allow
this. Since this change needs to be merged back, I want this
modification to be as small as possible.

BUG=709927

Review-Url: https://codereview.chromium.org/2810873005
Cr-Commit-Position: refs/heads/master@{#463814}
Committed:
https://chromium.googlesource.com/chromium/src/+/babffd17e43935e30657dcfda02d...
==========

[commit-bot: I haz the power, 2017-04-11 22:48:22]

Committed patchset #1 (id:1) as
https://chromium.googlesource.com/chromium/src/+/babffd17e43935e30657dcfda02d...